6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ning Ding [ Upstream commit dc36739e5cc9f60485418a910b42bc95339218d2 ] bpf_refcount_acquire() is fallible for a borrowed reference because the object may have reached a zero refcount. The verifier therefore keeps KF_RET_NULL on the return value unless the argument is an owning reference. An RCU-protected load of a local kptr is marked MEM_ALLOC, but it only receives NON_OWN_REF when the pointee contains a graph node. A refcounted object without a graph node consequently looks like an owning reference even though the loaded register has no acquired reference state. If the program drops the last real reference while remaining in the RCU critical section, refcount_inc_not_zero() returns NULL while the verifier treats the result as non-NULL. Only classify the argument as owning when it is backed by a verifier-tracked reference. This retains the non-NULL return for pointers from bpf_obj_new(), bpf_kptr_xchg(), or an earlier successful acquisition, while requiring a NULL check for borrowed RCU kptrs. Fixes: 1b12171533a9 ("bpf: Mark direct ld of stashed bpf_{rb,list}_node as non-owning ref") Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Ning Ding [ kkd: Rewrote commit log ] Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-4-memxor@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e887b6cc2cbae..9ed6a1298a8ec 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13812,7 +13812,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ verbose(env, "arg#%d is neither owning or non-owning ref\n", i); return -EINVAL; } - if (!type_is_non_owning_ref(reg->type)) + if (!type_is_non_owning_ref(reg->type) && reg->ref_obj_id) meta->arg_owning_ref = true; rec = reg_btf_record(reg); -- 2.53.0